An automated manual transmission is a system for automatically controlling a manual transmission. Unlike an automatic transmission that uses a torque converter and a wet-type multi-disk clutch, the automated manual transmission transmits an engine torque using a dry clutch.
Particularly, according to the dry clutch, a clutch transmission torque varies due to various factors from component errors, abrasion due to wear, thermal deformation caused by high temperature, to a variation in coefficient of friction of disks. Accordingly, it is difficult to estimate the transmitted torque while driving a vehicle.
When the variation in transmission torque is not detected when the clutch is being controlled, an algorithm for estimating torque characteristics of a dry clutch in real-time is necessary because excessive slip of the clutch or shock may occur in the clutch.
A conventional method estimates the clutch transmission torque through micro-slip control of a clutch, which predicts a torque-stroke (T-S) curve of the dry clutch in real time. The T-S curve illustrates a transmission torque characteristic of a dry clutch depending on a stroke of a clutch actuator.
For example, referring to FIG. 1, clutch speed and engine speed are controlled to maintain a micro-slip state by lowering a target torque of a clutch while a gearshift is engaged. Since an angular velocity of an engine is constant under the micro-slip condition, engine rotational inertia is not considered, and thus, the engine torque and the clutch torque are physically the same. Accordingly, the T-S curve may be obtained through the micro-slip control, which uses the engine torque and the stroke of the clutch actuator.
The characteristic of a dry clutch varies in real time, and thus, the micro-slip control is required continually for estimating the characteristic of the dry clutch so as to secure the operability and controllability of a dual-clutch transmission (DCT).
However, the micro-slip control causes a continuous small slip in the clutch, which may decrease durability of the clutch. In addition, since the engine RPM needs to be continuously controlled to be greater than 30 revolutions per minute (RPM), fuel efficiency may decrease.
In order to predict the T-S curve characteristic, continuous learning of the clutch torque is necessary, and thus, the micro-slip control should be continuously performed.
The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those skilled in the art.